Valve assemblies for adaptive and semi-active shock absorbers are comprised of a valve which is either slowly or speedily actuated. The valve varies the flow of fluid between the variable volume chambers of the shock absorber, thus accomplishing a fluid restriction to increase or decrease the damping coefficient, i.e., the damping level of the shock absorber. The valve assembly which is located within the shock body, can be actuated in any one of several manners. The first comprises actuating the valve by a motor or rotating means which is outside the shock body. This method usually is accomplished by mounting a motor atop the piston rod. The second encompasses integrating the motor or rotating means into the shock body. For example, the commonly assigned U.S. Pat. No. 4,838,392 to Miller et al., describes a semi-active shock absorber with an internal voice coil type valve.
In many current production systems, the motor is added atop the shock absorber as was first mentioned. Specifically, the stationary part of the motor, such as a stepper motor, is attached to the piston rod and the moving portion, or output shaft, is connected to a control rod. This control rod is then connected to a rotary valve. The control rod and valve which comprise the valve assembly are then actuated rotationally by actuation of the rotating means, such as a stepper motor or gear motor. A motor assembly of this type is described in U.S. Pat. No. 4,747,474 to Kimura et al.
Adaptive systems are slow acting systems which have valves that are typically actuated from outside the shock body. Adaptive systems only require valve response times that are actuated on the order of seconds (approximately 50 milliseconds or more). Semi-active systems require faster response times. Typically, the valve assembly must be actuated in milliseconds (approximately 50 milliseconds or less). This requires a valve assembly which has very low inertia and where the parasitic frictional and viscous forces acting on the valve assembly have been minimized. In this way, extremely fast valve response time can be obtained, and the motor power requirements can be minimized.